1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus, particularly, relates to a magnetron sputtering apparatus having a yoke-type permanent magnet, which enables higher target usable efficiency.
2. Description of the Related Arts
A magnetron sputtering apparatus has been commonly used as a sputtering apparatus until now.
FIG. 5(d) is a conceptional cross sectional view of a target formed with an erosion portion according to the conventional magnetron sputtering apparatus of the prior art.
FIG. 6(d) shows a measured cross sectional view of an erosion portion formed on the target exhibiting an actual erosion portion measured in the radial direction from the center of the target according to the conventional magnetron sputtering apparatus of the prior art.
FIG. 13 is a cross sectional view of a conventional magnetron sputtering apparatus according to the prior art. In FIG. 13, a conventional magnetron sputtering apparatus 19 is composed of a vacuum chamber 2, a target 3, a cathode 4, a substrate 5, an anode 6 and a yoke-type permanent magnet 79. The target 3 is placed on the cathode 4 and allocated inside the vacuum chamber 2. The substrate 5 is loaded on the anode 6 so as to face toward the target 3 on the cathode 4. The yoke-type permanent magnet 79 is provided under the cathode 4 for generating a magnetic field 149.
The yoke-type permanent magnet 79 is further composed of a base 8, a first yoke-type permanent magnet 99, which is fixed at the center portion of the base 8, and a second yoke-type permanent magnet 109 in a ring shape, which is fixed at the outer circumference area of the base 8 so as to surround the first yoke-type permanent magnet 99. In the first yoke-type permanent magnet 99, the top surface is the N-pole and the bottom surface is the S-pole. On the contrary, in the case of the second yoke-type permanent magnet 109, the top surface is the S-pole and the bottom surface is the N-pole. These top surfaces of the first and second yoke-type permanent magnets 99 and 109, that is, the top surfaces of the yoke type permanent magnet 79 are on the same plane. The magnetic field 149 generates from the N-pole side of the first yoke-type permanent magnet 99 and goes toward the S-pole side of the second yoke-type permanent magnet 109.
Operations of the magnetron sputtering apparatus 19 are explained next.
After gas such as Ar has been introduced into the vacuum chamber 2, high frequency electric power or large DC (direct current) power supplied from a not shown power source is applied to the cathode 4, and then plasma is generated. The generated plasma is trapped by the magnetic field 149. Since majority of the plasma is trapped at a portion where the magnetic field 149 is perpendicular to the surface of the target 3 particularly, plasma density becomes higher in the surface of the target 3 where the magnetic field 149 intersects vertically. Consequently, sputtering can be conducted efficiently.
However, as shown in FIG. 13, the portion of the target 3 where the plasma converged on is sputtered intensively, so that erosion portions 139a and 139b, which are scraped out deeply, are formed on the surface of the target 3 if the target 3 is used continuously. The conceptional cross section of the erosion portions 139a and 139b and their measured cross section are shown in FIG. 5(d) and FIG. 6(d) respectively. Consequently, the target 3 can not be used anymore although flat surfaces other than the erosion portions 139a and 139b are left in large areas.
In order to solve the above-mentioned problem, there exists the magnetron sputtering apparatus that is disclosed in the Japanese Patent Application Laid-open Publication No. 2002-069637.
The Japanese Patent Application Laid-open Publication No. 2002-069637 discloses the magnetron sputtering apparatus, wherein magnetic field generated by the first yoke-type permanent magnet 99 and the second yoke-type permanent magnet 109 are conducted to be different strength respectively and the apparatus is provided with a transfer device for moving the yoke-type permanent magnet 79 vertically in comparison with the magnetron sputtering apparatus 19 shown in FIG. 13.
However, cooling water is essential to be circulated in the cathode 4. Consequently, further problem occurs such that mechanism is very complicated in order to provide the transfer device, which moves vertically without leaking water.
Further, there exists a limit for improving target usable efficiency because a portion of the target 3 where the center magnetic pole of a permanent magnet is positioned is apt to become a non-erosion portion.